I converted a bike I bought off Craigslist for $200 plus an $850 Bafang kit off AliExpress. Didn’t have any experience with bike maintenance beforehand, but did have access to a makerspace with a full bike bench (there’s some specialized tools for pulling things out). Didn’t have it completely working before winter hit–works as a bike, but the motor assist isn’t kicking in for some reason–but I still think it’s an option most people could pull off.